A current area of development in wireless communications systems involves the use of transmitters and receivers having multiple antennas. Generally, these are known as multiple-input multiple-output (MIMO) systems and offer increased peak data rate, spectral efficiency, and quality of service through the use of a plurality of data streams
Relative to other wireless technologies, MIMO systems may enable substantial gains in both system capacity and transmission reliability without requiring an increase in frequency spectrum resources. By increasing the number of transmit and receive antennas, the capacity of a MIMO channel may be increased while also reducing the probability of all sub-channels between the transmitter and receiver fading simultaneously.
An access point (AP) may communicate with one or more stations (STAs) simultaneously using a multi-user (MU)-MIMO transmission. The AP may send an MU-MIMO transmission to a group of STAs (e.g., an MU group), in which the STAs are assigned a common group identifier (ID). However, some STAs in the MU group may have little or no traffic to receive at a particular time when an MU-MIMO transmission is scheduled and/or may have transmission characteristics substantially different from other STAs in the MU group. Such a disparity in traffic to be received by STAs in an MU group decreases wireless communication system efficiency and throughput. In addition, some MU-MIMO systems may include a relatively large number of STAs. Traffic disparity, transmission characteristics and large STA numbers may increase the difficulty of forming efficient MU-MIMO groups.